1. Technical Field
The disclosure relates to controlling fuel vapor purging of a hybrid electric vehicle as well as for performing adaptive learning of sensors providing information relevant to air-fuel ratio calculations.
2. Background Art
Engine fuel systems contain a carbon canister for collecting fuel vapors produced in the fueling system, in which fuel vapors adsorb onto carbon pellets within the carbon canister. The capacity of the carbon pellets for storing fuel vapors is finite. Thus, periodically, the carbon canister undergoes a purge process in which fresh air is drawn from the atmosphere into the carbon canister. The fuel vapors are desorbed from the carbon pellets and the vapor laden air is drawn into the engine where it is burned during engine combustion.
Engines also have air-fuel ratio control methods. In some operating modes, the engine is operated closed-loop to control air-fuel ratio. Closed-loop feedback control is based on a signal from an exhaust gas oxygen sensor in the engine exhaust. In other operating modes, air-fuel ratio is controlled open-loop based on signals from a sensor in the engine intake from which air flow rate can be computed and fuel pulse width commanded to the injectors from which fuel flow rate can be computed. Closed-loop control is preferred, but cannot always be used, e.g., when the exhaust gas oxygen sensor is cooler than its operating temperature, when the engine undergoes severe transients in which the delay from what is happening upstream of the engine to the exhaust gas oxygen sensor located in the exhaust stream is too long, and when the engine is operated at an air-fuel ratio away from stoichiometric. The sensors and actuators upon which the open-loop control relies to determine fuel and air flow rates vary from engine to engine and vary over time. To ensure accuracy of the open-loop control, closed-loop measurements are compared with open-loop measurements periodically. If a difference is detected, parameters in the open-loop computation are adjusted to account for the variability encountered.
Purging of the carbon canister provides fuel into the combustion chamber in excess of what is injected by fuel injectors. The amount of fuel injected by the injectors is decreased to compensate for the purge fuel. Because the fuel inducted into the engine is in excess of the injected fuel, if an adaption routine were conducted simultaneously with purging, the open-loop parameters would be inaccurate. Thus, purging is turned off when the adaption routine is conducted. It is found that to adequately purge the carbon canister, purging is commanded substantially whenever engine conditions allow it.
In the prior art, the adaption routine is commanded to run as soon as possible after the engine has been started, which impacts the time allowable for purging, but not substantially. In hybrid electric vehicles (HEVs), however, because the engine is stopped and started frequently to improve the vehicle's fuel efficiency, the adaption routine is run much more frequently than is strictly necessary and it presents a substantial obstacle to purging the carbon canister. The reduction in purge opportunities increases the likelihood that the carbon canister becomes saturated, which would potentially allow exhausting of fuel vapors from the carbon canister. This may negatively impact the ability of the vehicle to meet the relevant emission standards.